Shipping in the Strait of Hormuz is limited, but not closed. In the Red Sea, shipping could go a longer way around, but there is no alternative route for shipping in and out of the Persian gulf. This will likely increase the price of oil.
Iran could hit a US carrier with a hypersonic missile, but hitting a moving carrier and not getting shot down while the missile itself it moving and partially blinded by the plasma created by its extreme speeds…is very difficult, and it’s not clear how many of these missiles Iran has, or if they work.
Larger ships are vulnerable to modern weapons. With a larger ship, you have more eggs in one basket. If the enemy takes out that one ship, you’ve lost a lot of firepower. Even with anti-missile and anti-drone defenses, the enemy only needs one good hit.
The US is having trouble building its navy partially because it doesn’t have enough skilled people. It takes 8 years to get people fully up to speed, and it is having trouble keeping its aging workforce on the job.